1. Field of the Invention
The present invention relates to a charged-particle beam lithography apparatus using an electron beam or the like. More particularly, this invention is concerned with a blanking signal used to control the on-off operation of a charged-particle beam employed in a charged-particle beam lithography apparatus, and circuits handling the blanking signal.
2. Description of the Related Art
Owing to advances in fine processing technology, semiconductor integrated circuits tend to have circuit elements thereof integrated even more densely. The performance the fine processing technology is now required to offer is very high. Especially in a lithographic technology, a photolithographic technology adopted for an existing stepper will soon reach its limits. A charged-particle beam lithographic technology or especially an electron-beam lithographic technology is expected to produce the next generation of fine processing. How the throughput or reliability of fine processing should be improved is a technological obstacle to be overcome. An electron-beam lithography apparatus will be described as an example below. The present invention is not limited to the electron-beam lithography apparatus.
The electron-beam lithography apparatus is available in a variable rectangular lithography mode type, a block lithography mode type, and a multibeam lithography mode type. The present invention can be adapted to these modes. Herein, the block lithography mode will be described as an example. In the block lithography mode, a pattern that is a unit to be repeated for drawing graphics is delineated on a transparent mask. An electron beam is passed through the transparent mask. Delineated patterns are then transferred simultaneously and concatenated later. Thus, the repetitive graphics are drawn. One irradiation of an electron beam for transferring the unit pattern is called a shot. Herein, the term xe2x80x9cshotxe2x80x9d will be adopted.
The electron-beam lithography apparatus converges a reshaped electron beam on a sample, and controls the on-off operation of the electron beam while changing an irradiated position at which the electron beam is irradiated. The electron-beam lithography apparatus thus exposes the sample to transfer a desired pattern. For controlling the on-off operation of the electron beam, a blanking signal is applied to a blanking deflector. When the electron beam is irradiated (turned on), it will not be deflected. When the electron beam is not irradiated (turned off), it will be deflected and intercepted. In other words, the sample is exposed with the electron beam turned on. If an error occurs in exposure time (shot time), exposure will not be carried out in a desired manner. The exposure time must therefore be set very precisely. Moreover, the exposure time must coincide exactly with deflection of the electron beam.
According to a typical block lithographic mode, the number of times of electron-beam irradiation (number of shots) is as large as 10 M shots per chip or 1 G shots per wafer. The cycle of electron-beam irradiation is about 10 MHz. A clock generating circuit for generating a clock signal used for synchronization generates a blanking signal that is turned on or off at a very high rate equivalent to 10 MHz. The clock generating circuit then applies the blanking signal to a blanking deflector. An electron-beam lithography apparatus is realized with hardware including mechanisms such as a column and stage, an exposure control unit, and an analog amplifier (driver) for operating deflectors. A high voltage is employed in many components, and various kinds of noise therefore arise. The causes of noise are, for example, discharge occurring in high-voltage components or an electron gun, a noise occurring in a lens power source, charging of the column, and bit missing or incorrect latching occurring in a digital arithmetic circuit or amplifier included in an exposure control unit. As mentioned above, the blanking signal is a very important signal. If any noise occurs, a problem arises in that a beam may be twisted or a shot may be skipped. If this kind of abnormality occurs, the cause thereof must be investigated and the electron-beam lithography apparatus must be restored immediately to its normal state. In particular, as far as an electron-beam lithography apparatus employee in the process of mass production is concerned, a decrease in operation time of the apparatus leads directly to an increase in cost of production. An electron-beam lithography apparatus having an abnormality must be restored quickly. It is therefore required to detect occurrence of an abnormality immediately and locate the cause readily.
However, in electron-beam lithography apparatuses of related arts, the above abnormality is detected by inspecting actually transferred patterns or a semiconductor integrated circuit created on a wafer. Occurrence of the abnormality is recognized much later than lithography. This poses a problem in that many defects are manufactured until occurrence of an abnormality is recognized. Moreover, even if an abnormality is discovered, it is not easy to determine that the abnormality was caused by abnormal lithography. Too much time and labor are therefore needed to analyze the possible causes. In particular, the foregoing abnormal lithography is derived from noise or the like. Abnormal lithography does not therefore always occur and some kinds of abnormal lithography occur less frequently. It is very difficult to analyze these abnormalities.
An object of the present invention is to provide a charged-particle beam lithography apparatus and system capable of readily detecting an abnormality in controlling the on-off operation of a charged-particle (electron) beam employed in a charged-particle (electron) beam lithography apparatus, and readily finding out the cause of the abnormality.
A charged-particle beam lithography apparatus in accordance with the present invention attempts to accomplish the above object. A variation of a generated blanking signal is monitored, and a digital signal indicating the variation is produced. The digital signal is compared with exposure pattern data. Thus, it can be detected whether the on-off operation of a charged-particle beam is controlled according to the exposure pattern data.
Specifically, the charged-particle beam lithography apparatus, in accordance with the present invention, consists of a charged-particle beam generator, a charged-particle beam reshaping means, a charged-particle beam converging means, a charged-particle beam deflecting means, and a blanking means. The charged-particle beam generator generates a charged-particle beam. The charged-particle beam reshaping means reshapes the charged-particle beam. The charged-particle beam converging means converges the charged-particle beam on the surface of a sample. The charged-particle beam deflecting means deflects the charged-particle beam. The blanking means controls the on-off operation of the charged-particle beam. Herein, the blanking means includes a blanking signal generating circuit, a driver, and a blanking deflector. The blanking signal generating circuit generates a blanking signal used to control the on-off operation of the charged-particle beam according to exposure pattern data. The driver produces a driving signal according to the blanking signal. The blanking deflector deflects the charged-particle beam according to the driving signal so as to bring the charged-particle beam to a state in which it is intercepted by an intercepting means or a state in which it is not intercepted. The charged-particle beam lithography apparatus further consists of a digital converting circuit, and a comparing circuit. The digital converting circuit produces a blanking data signal that is a digital signal indicating a variation of the blanking signal from the blanking signal. The comparing circuit compares the blanking data signal with the exposure pattern data. It can be detected whether the on-off operation of the charged-particle beam is controlled according to the exposure pattern data.
In the charged-particle beam lithography apparatus in accordance with the present invention, the blanking signal is converted into a digital signal that can be compared with the exposure pattern data based on which the blanking data signal is produced. It can therefore be judged whether the charged-particle beam lithography apparatus is normal by comparing the change between the exposure pattern data and the digital signal converted from the blanking signal.
The blanking data signal is produced by converting an output of the blanking signal generating circuit or an output of the driver included in the blanking deflector. When the blanking data signal is produced from the output of the blanking signal generating circuit, it is detected whether the blanking signal generating circuit is normal. In this case, the exposure pattern data to be input to the blanking signal generating circuit is compared with the blanking data signal. The digital converting circuit and comparing circuit may be installed near the blanking signal generating circuit. When the blanking data signal is produced from the output of the driver, it is detected whether the blanking signal generating circuit, driver, and signal path between them are normal. In this case, the arrangement of the components will vary depending on where the driver is located. If the driver is located near the blanking signal generating circuit, the digital converting circuit and comparing circuit may be, as mentioned above, installed near the blanking signal generating circuit.
In contrast, the driver may be located far from the blanking signal generating circuit. The blanking signal may be transmitted from the blanking signal generating circuit to the driver over a first cable. In this case, the digital converting circuit is installed near the blanking signal generating circuit. The blanking signal transmitted to the driver over a second cable is converted in order to produce the blanking data signal. In this case, the driver is generally composed of a receiver for receiving the blanking signal transmitted from the blanking signal generating circuit and a drive circuit for producing a driving signal from an output of the receiver. The output of the receiver or the output of the drive circuit is transmitted to the digital converting circuit over the second cable. When the output of the receiver is transmitted, it is detected whether the blanking signal has been transmitted normally. When the output of the drive circuit is transmitted, it is also detected whether the driver is normal.
Furthermore, before the blanking signal is transmitted over the second cable, the blanking signal may converted into a digital blanking signal. Thus, the blanking signal may be transmitted in the form of a digital signal.
In the foregoing configuration, the exposure pattern data and blanking data signal are compared with each other in order to detected whether the blanking signal generating circuit, driver, and signal path between them are normal. Alternatively, it may be judged whether the produced exposure pattern data or blanking data signal is normal. In this case, limit data is pre-set. The limit data represents the limits of the exposure pattern data or blanking data signal. It is judged whether the produced exposure pattern data or blanking data signal exceeds the limit data. If the produced exposure pattern data or blanking date signal exceeds the limit data, it is judged to be abnormal. This abnormality detection may be carried out in combination with abnormality detection of detecting an abnormality in the blanking signal generating circuit, driver, and signal path between them.
The charged-particle beam lithography apparatus may be regarded as a column. A plurality of columns may be integrated into one system in an effort to improve throughput. A charged-particle beam lithography system for exposing a plurality of samples in parallel with one another to transfer the same exposure pattern is referred to as a multi-column system and is well known. The present invention may be adapted to the multi-column system. The multi-column system is provided with a synchronizing means for synchronizing actions of the columns with an action of a column that is the slowest to react on each processing. This is intended to adjust differences among the columns. In this case, one of the plurality of columns is regarded as a reference apparatus. The reference apparatus includes a coefficient memory and a comparing means. Differences in variation between the signal generated by a blanking signal generating circuit in the reference apparatus and the signals generated by blanking signal generating circuits in the other columns are measured in advance and stored as coefficients in the coefficient memory. The comparing means compares the variations of the signals, which are generated by the blanking signal generating circuits in the columns other than the reference apparatus, with the product of the variation of the signal, which is generated by the blanking signal generating circuit in the reference apparatus, by the coefficient. If the values disagree with each other or greatly differ from each other, it is judged that an abnormality has occurred.